JP2008299994A - Optical recording medium device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium device capable of preventing an increase in noise, a deterioration in a recording layer and erroneous elimination of data because information can be optimally reproduced in accordance with the classification of a changed medium D even though the number of layers and the reproducing speed of the optical recording medium D are changed. <P>SOLUTION: The optical recording medium device is provided with a laser driving circuit 26 for forming driving current Id obtained by superimposing high frequency current Irf on basic current Ib, a discrimination circuit 38 for discriminating the number of layers of a medium D on the basis of an output of a main detector 16, a control circuit 24 for outputting a control signal so as to change the current Ib in accordance with the number of layers and the reproducing speed of the medium D on the basis of an output that detects a portion of the laser beam and an output of the discrimination circuit, and a control part 40 for controlling a high frequency oscillator so as to change the amplitude of the current Irf in accordance with the number of layers of the medium D on the basis of the output of the discrimination circuit 38. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical recording medium device that reads information by irradiating an optical recording medium having a different number of recording layers (number of layers) such as a single-layer disc and a dual-layer disc.

  In general, optical discs (hereinafter referred to as “optical recording media”) such as DVD (Digital Versatile Disc) and BD (Blu-ray Disc) are known as recording media having a large storage capacity. In order to increase the storage capacity of the recording medium, there has been proposed an optical recording medium in which not only one recording layer but also two or more recording layers are provided.

  Correspondingly, in an optical recording medium reproducing apparatus for recording or reproducing information with respect to the optical recording medium, an optical recording medium having a plurality of recording layers is also used for an optical recording medium having a single recording layer. An optical recording medium reproducing apparatus that reproduces information recorded on a recording layer by irradiating a recording medium with laser light from a semiconductor laser element via an optical system to each recording layer has been proposed.

  However, in reality, when a part of the laser light irradiated to the optical recording medium by the semiconductor laser element is reflected by the recording layer of the optical recording medium and returns to the semiconductor laser element, the return light is changed in power of the semiconductor laser element. There is a problem that the reproduced video and audio signals are affected. The power fluctuation of the semiconductor laser element is also caused by temperature fluctuation.

  Therefore, a high-frequency superposition method for superposing a high-frequency current on the basic current of the semiconductor laser element is used as the most simple and effective method for reducing the noise as described above (see, for example, Patent Documents 1 and 2). .

On the other hand, a method for changing the constant of the snubber circuit according to a plurality of types of optical recording media has been disclosed (for example, see Patent Document 3).
JP-A-62-1119743 Japanese Patent Laid-Open No. 62-287445 JP-A-2005-346868

  However, in the conventional techniques described in Patent Documents 1 and 2 described above, noise is suppressed by superimposing a high-frequency current on the basic current of the semiconductor laser element, but the amplitude (level) of the superposed high-frequency current remains constant. Therefore, when the number of layers of the optical recording medium is changed, the waveform and peak level of the drive current on which the high-frequency current is superimposed change, so that the effect of superposition of the high-frequency current is reduced and noise is increased. On the contrary, there is a problem that the superposition level of the high-frequency current is too large and the peak level becomes high, which causes deterioration of the recording layer and erroneous erasure of data.

  Further, in the conventional technique described in Patent Document 3 described above, since the superposition level of the high frequency current is changed by changing the time constant of the snubber circuit, the current consumed by the snubber circuit is increased and unnecessary radiation is increased. There was a problem.

  The present invention has been made in view of such a problem. When the number of layers of the optical recording medium is changed (that is, from a single-layer optical recording medium to a multi-layer optical recording medium, or from a multi-layer optical recording medium). Even when the type of the optical recording medium is changed to a single-layer optical recording medium, it is possible to prevent an increase in noise caused by this, and the reproduction speed of the optical recording medium is low (for example, BD 1 × or BD 2 ×). ) Or high speed (BD 4 × speed), an object of the present invention is to provide an optical recording medium device that can prevent an increase in noise and prevent deterioration of a recording layer and erroneous erasure of data.

  In order to solve the above problems, the present invention provides an optical recording medium device having the following configurations (1) to (3).

(1) As shown in FIG. 1 and FIG. 7, a laser drive current Id in which ringing and overshoot are suppressed using a snubber circuit (configured by a resistor Rs and a capacitor Cs connected in series) (FIG. 7) is a semiconductor. The laser light supplied to the laser element LD and emitted from the semiconductor laser element LD is a single layer (one layer) or a plurality of layers (two layers) of the recording layer Dr (shown in FIG. 1 is a single recording layer Dr). An optical recording medium device A (FIG. 1) having a configuration for reading information by irradiating on an optical recording medium D having
A laser light emitting circuit (semiconductor laser element and snubber circuit) 2 that includes the snubber circuit and the semiconductor laser element LD, and emits recording or reproducing laser light through the objective lens 10;
A main light detector 16 for detecting reflected light obtained by irradiating the optical recording medium D with laser light emitted from the laser light emitting circuit 2 and outputting a main detection signal according to the light reception level;
Based on a main detection signal output from the main light detector 16, a discrimination signal for determining at least the number of recording layers of the optical recording medium D (the number of recording layers and the low-speed / high-speed playback speed) is output. The number of layers discriminating circuit 38,
A secondary light detector 18 for detecting a part of the laser light emitted from the laser light emitting circuit 2 and outputting a secondary detection signal;
Based on the discrimination signal output from the layer number discrimination circuit 38 and the sub-detection signal output from the sub-photodetector 18, the laser beam is set so that the output power of the light emitted from the semiconductor laser element LD is constant. A drive control signal output circuit (drive control circuit) 24 for outputting a drive control signal Sa to the input side of the emission circuit 2;
A high-frequency oscillator 28 is provided, and a basic current Ib for driving the semiconductor laser element LD is formed based on a drive control signal Sa output from the drive control signal output circuit 24, and the high-frequency oscillator 28 is added to the formed basic current Ib. A laser drive circuit 26 for outputting a laser drive current Id obtained by superimposing the high-frequency current Irf output from the oscillator 28 to the laser beam emitting circuit 2;
A high-frequency oscillator control circuit (high-frequency oscillator control unit) 40 that outputs a control signal for changing the output current amplitude of the high-frequency oscillator 28 to the high-frequency oscillator 28 based on a determination signal output from the number-of-layers determination circuit 38; Have
The layer number discriminating circuit 38
When the optical recording medium D is determined as a single-layer optical recording medium, a determination signal for operating the snubber circuit and reducing the output current of the high-frequency oscillator 28 is sent to the laser light emitting circuit 2 and the Each output to the high frequency oscillator control circuit 40,
When the optical recording medium D is discriminated as an optical recording medium having a plurality of layers and being reproduced at a low speed, a discrimination signal for deactivating the snubber circuit and reducing the output current of the high-frequency oscillator 28 is sent to the laser. Output to the light emitting circuit 2 and the high-frequency oscillator control circuit 40, respectively.
Further, when the optical recording medium D is determined to be an optical recording medium having a plurality of layers and reproducing at a higher speed than the low-speed reproducing, the snubber circuit is deactivated and the output current of the high-frequency oscillator 28 is compared with the small oscillation. An optical recording medium device characterized in that a discrimination signal for large oscillation is output to the laser beam emitting circuit 2 and the high-frequency oscillator control circuit 40, respectively.

(2) As shown in FIG. 1, the high-frequency oscillator control circuit 40 includes:
Switching means (switching transistor Tr) that is turned on / off based on a discrimination signal output from the layer number discrimination circuit 38;
The resistance value is changed by turning on / off the switching means Tr, and the amplitude of the high-frequency current Irf output from the high-frequency oscillator 28 is controlled to change according to the number of layers of the optical recording medium D (resistances Rf, Ra1, 2. The optical recording medium device according to claim 1, further comprising high-frequency current amplitude switching means (consisting of Ra2).

(3) As shown in FIG.
A snubber circuit control unit (consisting of switching transistors Tr1 and Tr2) for controlling the snubber circuit;
The snubber circuit control unit includes switching means (switching transistors) Tr2 and Tr3 that are turned on / off based on a determination signal (snubber ON / OFF signal) output from the layer number determination circuit 38;
When the switching means Tr2 and Tr3 are turned on / off, the snubber circuit composed of a resistor Rs and a capacitor Cs is connected in parallel with the semiconductor laser element LD, and is output from the high-frequency oscillator 28 to the semiconductor laser element LD. 2. The optical recording medium device according to claim 1, further comprising high frequency current amplitude switching means (configured by a resistor Rs and a capacitor Cs) for controlling the amplitude of the flowing high frequency current Irf to change.

  According to the optical recording medium device of the present invention, when the high-frequency current from the high-frequency oscillator is superimposed on the basic current and output as the drive current to the semiconductor laser element, the output from the sub-light detector and the output of the layer number discrimination circuit Based on the above, the basic current is controlled to change according to the number of layers of the optical recording medium (only when it is determined that the optical recording medium is compatible with multiple layers (two layers) and high-speed reproduction). And control so that the amplitude of the high-frequency current changes according to the number of layers of the optical recording medium and the reproducing speed based on the output of the layer number discrimination circuit (single layer optical recording medium) When it is determined that the snubber circuit is in parallel connection with the semiconductor laser element, control is performed so that the snubber circuit is not in parallel connection with the semiconductor laser element when it is determined that the optical recording medium is a multi-layer optical recording medium. Since the way, both possible to prevent the noise at the time of reading of information is increased, it is possible to prevent erroneous erasure of deterioration and the data of the recording layer.

  In addition, by controlling the snubber circuit in parallel connection with the semiconductor laser element, it is possible to further reduce noise than the minimum high-frequency current from the high-frequency oscillator. Can be expanded.

  Hereinafter, an embodiment of an optical recording medium device according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram of a reproducing system showing an embodiment of an optical recording medium device according to the present invention.

  In the optical recording medium apparatus A shown in FIG. 1, D is an optical recording medium such as a DVD or a Blu-ray disc (hereinafter referred to as “BD”), 2 is a semiconductor laser element and a snubber circuit, 3 and 4 are collimator lenses, and 6 is a beam. The beam splitter 6 is an optical component that combines a semi-transparent half mirror and a prism with respect to the laser light L.

  8 is a quarter wave plate, 10 is an objective lens, 12 and 14 are condensing lenses, 16 is a main light detector, 18 is a secondary light detector, 20 and 22 are amplifiers, and 24 is a drive control circuit (APC). Automatic Power Control), 26 is a laser drive circuit, 28 is a high-frequency oscillator, 30 is a polarization beam splitter, 32 is a drive motor for moving the collimator lens 4, 34 is a diffraction grating, and 36 is a signal reproduction system. The signal reproduction system 36 includes a reproduction signal processing circuit that forms a reproduction signal based on an output from the main light detector 16, a servo control circuit that forms a tracking error signal, and the like (none of which are shown). . Reference numeral 38 denotes a layer number discriminating circuit for discriminating the number of layers of the optical recording medium, for example, a single layer or two layers, and 40 denotes a high frequency oscillator control unit.

  In the present embodiment, the high-frequency oscillator control unit 40 includes a resistor Rf that determines the frequency of the high-frequency current generated by the high-frequency oscillator 28, and an amplitude setting resistor unit 50 that determines the amplitude (level) of the high-frequency current. have. The resistance value of the resistance means 50 and the amplitude of the high-frequency current generated by the high-frequency oscillator 28 are set so as to have an inversely proportional relationship. Therefore, as the resistance value increases, the amplitude of the high-frequency current decreases (small swing). Conversely, when the resistance value decreases, the amplitude of the high-frequency current increases (large swing).

  Here, the resistance means 50 includes a parallel connection circuit of a first resistor Ra1 and a second resistor Ra2, and the second resistor Ra2 is a switching element that is on / off controlled. For example, the switching transistor Tr Are connected in series.

  In the case of the present embodiment, the switching transistor Tr is on / off controlled by a signal from the layer number discrimination circuit 38. As will be described later, for example, when information recorded on the two-layer optical recording medium D is reproduced at high speed (for example, “BD 4 × speed reproduction”), the information recorded on the single-layer optical recording medium D is controlled. And when information recorded on the two-layer optical recording medium D is reproduced at a low speed (for example, “BD 1 × speed” or “BD 2 × speed” playback).

  The optical system 42 is constituted by each member provided in the optical path of the laser light L from the semiconductor laser element LD that constitutes the semiconductor laser element and the snubber circuit 2, and the part mainly composed of the objective lens 10 is the light. The pickup 44 becomes.

  FIG. 7 is a diagram illustrating a circuit example of the snubber circuit.

  As shown in FIG. 7, a circuit configured by connecting a resistor Rs and a capacitor Cs in series is called a snubber circuit. The snubber circuit is known as a circuit that suppresses ringing and overshoot of a laser drive current waveform during recording, which is generated by circuit wiring and the parasitic inductance of the semiconductor laser LD.

  For example, the switching transistors Tr <b> 2 and Tr <b> 3 that are switching elements are ON / OFF controlled by a snubber ON / OFF signal from the layer number discrimination circuit 38. For example, when information recorded on the single-layer optical recording medium D is reproduced, the control is turned on. When information recorded on the two-layer optical recording medium D is reproduced, the control is turned off. When the switching transistors Tr2 and Tr3 are turned on, the snubber circuit is connected in parallel with the semiconductor laser element LD. Since a high-frequency component current flows through the snubber circuit, when the current driven from the high-frequency oscillator 28 is constant, the high-frequency current flowing through the semiconductor laser element and the snubber circuit 2 is attenuated by the amount absorbed by the snubber circuit. .

  Next, the operation of the reproduction system block configuration of the above-described apparatus of the present invention will be described.

  The laser light L output from the semiconductor laser element and the snubber circuit 2 is incident on the polarization beam splitter 30 through the collimator lens 3 that converts the divergent light into parallel light and the diffraction grating 34 that splits the light beam into three. Predetermined polarized light is reflected toward the objective lens 10 on the bonding surface. The reflected light is condensed on the surface of the recording layer Dr of the optical recording medium D through the collimator lens 4, the beam splitter 6, the quarter wavelength plate 8 that converts linearly polarized light into circularly polarized light, and the objective lens 10. Here, in the case where the optical recording medium D is a two-layer optical recording medium, the objective lens is determined by the difference in the substrate thickness to the recording layer (the recording layer (second recording layer) at the back as viewed from the optical recording medium surface). Since spherical aberration occurs at 10, the spherical aberration is corrected by moving the position of the collimator lens 4 by driving the drive motor 32.

  The laser light applied to the optical recording medium D is reflected on the optical recording medium D, and this reflected light is incident on the quarter-wave plate 8 through the objective lens 10. The reflected light incident on the quarter wavelength plate 8 is converted into linearly polarized s wave whose polarization plane is orthogonal to the p wave at the time of irradiation, and is incident on the polarization beam splitter 30. The linearly polarized light that has entered the polarization beam splitter 30 is an s wave, so it is transmitted and incident on the condensing lens 14, where it is condensed and received by the main light detector 16. The light received by the main light detector 16 is converted into an electric signal having a level corresponding to the received light level, and is supplied to a signal reproduction system 36 having a reproduction signal processing circuit and a servo control circuit via an amplifier 20. In the reproduction system 36, it is used for detection of a recording information signal and detection of a focus error signal and a tracking error signal.

  The objective lens 10 is held by an actuator (not shown), and the objective lens 10 is driven in the focusing direction and the tracking direction by flowing the focus error signal and the tracking error signal through a focus coil and a tracking coil (not shown) in the actuator, respectively. Thus, it follows the track of the optical recording medium D.

  Further, based on the output from the main light detector 16 via the amplifier 20, the number-of-layers discrimination circuit 38 discriminates the type of the optical recording medium D, for example, how many recording layers it has, and uses this result as a high frequency signal. Output to the oscillator control unit 40 and the drive control circuit 24. This discrimination process is performed prior to reproduction of the optical recording medium D.

  The high frequency oscillator control unit 40 controls the high frequency oscillator 28 of the laser drive circuit 26 according to the number of recording layers of the optical recording medium D, as will be described later.

  Specifically, it is as follows. That is, when the optical disc recording medium D is discriminated as a single-layer optical recording medium, the layer number discriminating circuit 38 generates a discriminating signal for operating the snubber circuit and making the output current of the high-frequency oscillator 28 small. Output to the laser element and snubber circuit 2 and the high-frequency oscillator controller 40, respectively.

  Further, when the optical recording medium D is determined to be a multi-layer and low-speed reproducing optical recording medium, the number-of-layers determination circuit 38 determines that the snubber circuit is disabled and the output current of the high-frequency oscillator 28 is reduced. The signals are output to the semiconductor laser element and snubber circuit 2 and the high-frequency oscillator control unit 40, respectively.

  Further, when the layer number discriminating circuit 38 discriminates the optical recording medium D as an optical recording medium having a plurality of layers and reproducing at a speed higher than that at a low speed, the snubber circuit is deactivated and the output current of the high-frequency oscillator 28 is set to A discrimination signal for making a large oscillation (compared with oscillation) is output to the semiconductor laser element and snubber circuit 2 and the high-frequency oscillator control unit 40, respectively.

  By the way, a part of the laser beam L directed to the objective lens 10 is extracted by the beam splitter 6, and the extracted laser beam is detected by the auxiliary light detector 18 through the condenser lens 12. The detection signal detected by the auxiliary light detector 18 is amplified by the amplifier 22 and input to the drive control circuit 24.

  In the drive control circuit 24, the detection signal detected by the sub-light detector 18 and amplified by the amplifier 22 as described later, and the signal indicating the number of recording layers of the optical recording medium D from the layer number discrimination circuit 38 are used. Thus, the basic current output from the amplifier 26a of the laser drive circuit 26 is controlled.

  Specifically, in the drive control circuit 24, the laser drive circuit is configured so that the output power from the semiconductor laser element and the snubber circuit 2 is constant based on the detection signal detected by the sub-light detector 18 and amplified by the amplifier 22. The drive control signal Sa is output to 26. The laser drive circuit 26 forms a basic current Ib for driving the laser element by an amplifier 26a based on the drive control signal Sa, and superimposes the high-frequency current Irf generated by the high-frequency oscillator 28 on the basic current Ib, thereby driving the drive current. Id is formed, and the semiconductor laser element and the snubber circuit 2 are driven by this drive current Id. At this time, the drive control circuit 24 of the present embodiment responds to the signal indicating the number of recording layers of the optical recording medium D from the layer number discrimination circuit 38, and the basic current output from the amplifier 26a of the laser drive circuit 26. Ib is controlled.

  Here, a high-frequency current and a drive current formed by the laser drive circuit 26 having the high-frequency oscillator 28 will be specifically described with reference to FIGS.

  FIG. 2 is a diagram showing the relationship between the high-frequency current and the laser emission waveform for the recording / reproducing type two-layer high-speed optical recording medium D. That is, FIG. 2 shows the drive current Id at the time of laser light emission supplied to the semiconductor laser element and the snubber circuit 2 and the irradiation laser power characteristic on the surface of the recording layer Dr of the optical recording medium D (hereinafter referred to as “disk surface laser power characteristic”). ), And the relationship between the basic current Ib and the high-frequency current Irf forming the drive current Id and the laser emission waveform.

  FIG. 3 is a diagram showing the relationship between the high-frequency current and the laser emission waveform for the optical recording medium D that supports recording / reproducing single-layer high-speed or recording / reproducing double-layer low speed. That is, FIG. 3 shows the relationship between the drive current Id at the time of emitting the laser beam supplied to the semiconductor laser element and the snubber circuit 2 and the disk surface laser power characteristics, the basic current Ib that forms the drive current Id, the high-frequency current Irf, and the laser emission. The relationship with the waveform is shown respectively.

  As shown in FIGS. 2 and 3, the drive current Id is formed by superimposing the high-frequency current Irf on the basic current Ib which is a direct current. That is, the basic current Ib becomes the center level of the high-frequency current Irf. Here, for example, about 400 MHz is used as the frequency of the high-frequency current Irf. The semiconductor laser element LD outputs laser light at a threshold current Ith or more, and the laser emission waveform at that time is a waveform similar to a half-wave rectification waveform as shown in FIGS.

  The laser output power drive control of the semiconductor laser element and the snubber circuit 2 will be described. In FIG. 1, the light received by the sub-light detector 18 is converted into an electric signal having a level corresponding to the average amount of received light, and drive control is performed. A drive control signal Sa is fed back to the laser drive circuit 26 via the circuit 24. At this time, as described above, the drive control circuit 24 controls the basic current Ib output from the amplifier 26a of the laser drive circuit 26 according to the number of recording layers Dr of the optical recording medium D.

  The laser drive circuit 26 adjusts the output power by forming the basic current Ib based on the drive control signal Sa from the drive control circuit 24. As a result, the output power of the laser light emitted from the semiconductor laser element and the snubber circuit 2 is stabilized according to the number of recording layers Dr of the optical recording medium D.

  In the present embodiment, as described above, the high-frequency current Irf is superimposed on the basic current Ib in order to suppress the generation of laser noise caused by a part of the laser light returning to the semiconductor laser element and the snubber circuit 2. An actual drive current Id is formed.

  Here, the frequency and level (amplitude) of the superimposed high-frequency current Irf are set by the values of, for example, the resistor Rf and the amplitude setting resistor means 50 provided in the high-frequency oscillator control unit 40. . That is, the resistor Rf determines the frequency of the high-frequency current Irf, and the resistance means 50 including the resistors Ra1 and Ra2 determines the level. As shown in FIG. 2, the semiconductor laser element LD hardly emits light below the threshold current Ith. Therefore, as shown in FIG. 2, the characteristics of current-optical output (disk surface laser power) are maintained almost linear from the threshold current Ith, and the linearity is lost at a rated current (not shown).

  The semiconductor laser element LD is driven by the drive current Id formed by superimposing the high-frequency current Irf on the basic current Ib, that is, driven by the high-frequency current Irf that vibrates positively and negatively around the current value of the basic current Ib. The semiconductor laser element LD emits light when the current exceeds the current Ith, and the semiconductor laser element LD turns off when the current is less than or equal to the threshold current Ith. As a result, laser emission with a half-wave rectified waveform as shown in FIG. A waveform is formed. In addition, Pr is an average value of the laser power to the optical recording medium D surface (recording layer Dr surface).

  In the example shown in FIG. 2, the peak-to-peak power of the high-frequency current Irf superimposed on the basic current Ib is set to 52 mA, and the reproduction power of the optical recording medium D corresponding to the recording / reproducing type two-layer high speed is the average of the disk surface laser power. The value Pr is set to 0.8 mW. The disk surface peak power of the high-frequency current superimposing component is 2.6 mW, and when the recording layer is two layers, the peak power is not too high. Therefore, the recording layer in the optical recording medium D is deteriorated or data is erased erroneously. Does not occur, and the peak power is not too low, so that the effect of superposition of the high-frequency current is reduced and noise is not increased.

  On the other hand, when the recording layer is an optical recording medium D that supports two-layer low speed or single-layer high speed, the average value Pr of the disk surface laser power is 0 as the reproduction power of the optical recording medium D, as shown in FIG. Since the basic current Ib is controlled by the drive control circuit 24 and is lower than that in the case of the two-layer high speed, if the value of the resistance means 50 is a fixed value, the high frequency of about 400 MHz to be superimposed is set. The amplitude of the current Irf is the same as in the case of the optical recording medium D corresponding to the two-layer high speed (FIG. 2).

  Thus, the semiconductor laser element LD is driven by the drive current Id in which the high-frequency current Irf is superimposed on the basic current Ib, emits light when the drive current Id exceeds the threshold current Ith, and turns off when it is less than or equal to the threshold current Ith. The laser emission waveform shown in FIG. 3 is formed.

  When the recording layer is a single-layer high-speed or double-layer low-speed optical recording medium like the optical recording medium D shown in FIG. 3, the basic current Ib applied to the double-layer high-speed optical recording medium shown in FIG. Since the high-frequency current Irf having the same amplitude is superimposed even though it is lower, the high-frequency superimposed pulse width W2 shown in FIG. 3 is narrower than the high-frequency superimposed pulse width W1 shown in FIG. The peak power ratio of the high frequency superimposed component to the power Pr is increased.

  That is, in the case of the two-layer high-speed optical recording medium shown in FIG. 2, the average power Pr is 0.8 mW, the high-frequency superimposed component = the disk surface peak power of the high-frequency current Irf is 2.6 mW, and the average power Pr of the high-frequency superimposed component. In the case of the single-layer high-speed or double-layer low-speed optical recording medium shown in FIG. 3, the average power Pr of the high-frequency superimposed component is 0.5 mW, and the high-frequency superimposed component disk The surface peak power is 2.1 mW, and the ratio of the peak power to the average power Pr of the frequency superimposed component is 4.2. As a result, the optical recording medium shown in FIG. 3 is the same as the optical recording medium shown in FIG. In comparison, the ratio of the peak power to the average power Pr of the high frequency superimposed component is increased.

  Here, compared with a two-layer high-speed optical recording medium, a single-layer high-speed or two-layer low-speed optical recording medium has a recording sensitivity close to about 1.6 times, so that the disk surface peak power is 2.1 mW. The disk surface peak power is too high for a single-layer high-speed optical recording medium. In this case, the recording layer may be deteriorated or data may be erroneously erased, which is not preferable.

  Therefore, in this embodiment, when the optical recording medium D is a single-layer high-speed optical recording medium, the amplitude of the high-frequency current Irf superimposed on the basic current Ib is lower than that in FIG. 3, as shown in FIG. Control.

  FIG. 4 is a diagram showing the relationship between the high-frequency current and the laser emission waveform for the recording / reproducing single-layer high-speed optical recording medium D. That is, FIG. 4 shows the relationship between the drive current Id when the laser beam is supplied to the semiconductor laser element and the snubber circuit 2 and the disk surface laser power characteristics, the basic current Ib and the high-frequency current Irf when the drive current Id is formed. The relationship with the laser emission waveform is shown respectively.

  As described above, the drive current Id is formed by superimposing the high-frequency current Irf on the basic current Ib that is a direct current, and the basic current Ib becomes the center level of the high-frequency current Irf. Here, for example, about 400 MHz is used as the frequency of the high-frequency current Irf. Since the semiconductor laser element LD outputs laser light at a threshold current Ith or higher, the laser emission waveform is a waveform similar to a half-wave rectification waveform.

  Here, the drive control of the semiconductor laser element and the snubber circuit 2 will be described.

  In FIG. 1, the light received by the auxiliary light detector 18 is converted into an electric signal having a level corresponding to the average amount of received light, and becomes a drive control signal Sa via the drive control circuit 24 to the laser drive circuit 26. Returned. In the laser drive circuit 26, the output power is adjusted by forming the basic current Ib based on the drive control signal Sa. As a result, the output power of the laser light emitted from the semiconductor laser element and the snubber circuit 2 is stabilized. As described above, in order to suppress the laser noise that causes a part of the laser light to return to the semiconductor laser element and the snubber circuit 2, the high-frequency current Irf is superimposed on the basic current Ib, and the actual drive current Id. Form.

  The frequency and level of the high-frequency current Irf superimposed on the basic current Ib are set by the values of the resistor Rf provided in the high-frequency oscillator control unit 40 and the amplitude setting resistor means 50 as described above. That is, the resistance Rf determines the frequency of the high-frequency current Irf, and the resistance means 50 determines the level.

  Next, the operation of the resistance means 50 for setting amplitude will be described. The level of the high-frequency current Irf is determined by the resistance means 50 connected to the laser driving circuit 26, that is, the first resistance Ra1 and the second resistance Ra2, and the transistor switch Tr.

  Then, when reproducing the recording / reproducing type two-layer high-speed optical recording medium D, the transistor Tr is turned on by a command from the layer number discrimination circuit 38, and the first resistor Ra1 and the second resistor Ra2 are connected in parallel. The level of the high-frequency current Irf is determined by the resistance value. The resistance value of the parallel connection of the first resistor Ra1 and the second resistor Ra2 and the amplitude of the high-frequency current Irf are approximately inversely proportional. In this case, the first resistor Ra1 and the second resistor Ra2 are connected in parallel. By connecting to, the parallel resistance value is reduced as compared with the case of only the first resistor Ra1, so that the amplitude of the high-frequency current Irf is increased. The laser emission waveform at this time is formed as shown in FIG.

  On the other hand, when reproducing the single-layer high-speed or double-layer low-speed optical recording medium D, the transistor Tr is turned off by a command from the layer number discrimination circuit 38, and the second resistor Ra2 is opened. Therefore, the amplitude of the high-frequency current Irf is determined only by the first resistor Ra1.

  Therefore, when reproducing the single-layer high-speed or double-layer low-speed optical recording medium D, the resistance value of the resistance means 50 is increased as compared with the case where the first resistor Ra1 and the second resistor Ra2 are connected in parallel. . As a result, since the resistance value and the amplitude of the high-frequency current Irf are approximately inversely proportional, the resistance value of the resistance means 50 increases, so the amplitude of the high-frequency current Irf decreases. Therefore, in this embodiment, when reproducing the single-layer optical recording medium D, the laser emission waveform is formed as shown in FIG.

  That is, when reproducing the single-layer optical recording medium D, the drive control circuit 24 receives the optical recording medium D from the layer number discrimination circuit 38 so that the average value Pr of the disk surface laser power becomes the target 0.5 mW. Based on an indication of the number of layers (single layer) and a part of the laser power detected by the sub-light detector 18, the basic current Ib is controlled to be about 32 mA.

  In the high frequency oscillator control unit 40 of the present embodiment, as shown in FIG. 4, the high frequency current Irf of the AC sine wave has a peak-to-peak current of about 32 mA around the basic current Ib of about 32 mA DC current. The high frequency oscillator 28 is controlled so as to be driven. The semiconductor laser element LD emits light for a current exceeding the threshold current Ith, in this case about 35 mA, according to the characteristics of drive current versus disk surface laser power.

  As a result, in the case shown in FIG. 4, the disk surface peak power of the high frequency superimposed component is about 1.6 mW and the average power Pr is 0.5 mW, and the high frequency superimposed pulse width W2 has a peak power ratio with respect to the average power Pr. 3.25, which is the same as shown in FIG.

  As described above, in the present embodiment, since the amplitude of the high-frequency current Irf is appropriately switched according to the layer (single layer or two layers) of the optical recording medium D to be read, the single-layer optical recording medium D is reproduced. In this case, as shown in FIG. 4, the high frequency superimposed pulse width W3 is the same as the high frequency superimposed pulse width W1 at the time of reproducing the two-layer optical recording medium shown in FIG. The disk surface peak power of the high-frequency superimposed component is about 1.6 mW, which is 1 / 1.6 of about 2.6 mW of the disk surface peak power when the two-layer optical recording medium shown in FIG. Even when the recording layer reproduces a single-layer optical recording medium, the peak power is not too high, and the recording layer is not deteriorated and the data is not erased erroneously.

  In other words, unless the amplitude Irf of the high frequency current superimposed on the basic current Ib is changed according to the number of layers of the optical recording medium D, when reproducing a single-layer high-speed optical recording medium, as shown in FIG. Since the amplitude of the high-frequency current Irf is large, the peak value of the disk surface laser power is as high as 2.1 mW, which causes deterioration of the recording layer and erroneous data erasure.

  On the other hand, in the case of the present embodiment, as shown in FIG. 4, the amplitude (level) of the high-frequency current Irf superimposed on the basic current Ib is changed according to the number of layers and the speed of the optical recording medium D. In the case of a two-layer low-speed optical recording medium, the recording sensitivity is 1.6 times that of a two-layer high-speed optical recording medium, so that the average value Pr of the disk surface laser power is about 0.8 mW when the two-layer high-speed optical recording medium is used. Since the amplitude (level) of the high-frequency current Irf is changed so as to be half of 0.5 mW, the disk surface laser power peak value can be lowered to 1.6 mW, and the recording layer is deteriorated and data is erroneously erased. Can be prevented.

  Next, in the case of a single-layer low-speed optical recording medium, as shown in FIG. 5, the laser drive circuit 26 sets the disk surface laser power peak value of the high frequency superimposed current to 0.8 mW and the average power Pr to 0.25 mW. Therefore, it is necessary to reduce the high frequency superimposed current amplitude. The high frequency superimposed current amplitude characteristic of the laser drive circuit 26 may be a case where the minimum level has a limit and the amplitude does not decrease to a required level as shown in FIG.

  Therefore, in the case of the present embodiment, the snubber circuit is turned on even during reproduction, and a high-frequency component current is passed through the snubber circuit, so that the high-frequency current Irf flowing through the semiconductor laser LD is absorbed by the snubber circuit. It will be attenuated by the amount. Therefore, it is possible to make the amplitude less than the minimum level of the high-frequency superimposed current amplitude possible with the laser drive circuit 26. Under this condition, the high-frequency superimposed current is at a low level, so unnecessary radiation is not a problem.

  FIG. 6 is a diagram showing values of electric power and current when information of the single-layer and double-layer optical recording media D is reproduced according to the present embodiment. The average value Pr (mW) of the disk surface laser power, the output power (mW) of the semiconductor laser element 2, and the peak-to-peak current (mA) of the high-frequency current are each 0.25 mW in the case of a single-layer low-speed optical recording medium. 2.2 mW and 16 mA, which are 0.5 mW, 4.4 mW, and 32 mW in the case of a two-layer low-speed or single-layer high-speed optical recording medium, respectively. Further, in the case of a two-layer high-speed optical recording medium, the values are 0.8 mW, 7.0 mW, and 52 mW, respectively.

  As described above, according to the optical recording medium device of the present invention, the disk surface laser power, that is, the reproduction average light quantity (DC), which is the output of the semiconductor laser element and the snubber circuit, is changed according to the number of layers and the speed of the optical recording medium. In addition, even if the number of layers and the speed of the optical recording medium change, the high-frequency superimposition according to the number of layers and the speed of the optical recording medium is such that the peak power ratio of the high-frequency superimposed component to the average power of the high-frequency superimposed current is substantially constant. Since the amplitude (power) of the current is set to an optimum value, even when the number of layers of the optical recording medium D to be reproduced changes, the effect of superposition of the high-frequency current is reduced and noise is increased or vice versa. In addition, it is possible to prevent the superposition level of the high-frequency current from being too large and the peak level to be high, thereby deteriorating the recording layer and erroneous data erasure.

  It should be noted that the numerical examples used in this embodiment are merely examples, and of course are not limited thereto.

  Here, the resistor group is used to change the amplitude of the high-frequency current Irf. However, the present invention is not limited to this, and any means may be used as long as the amplitude can be changed, such as a capacitor. May be used.

  Further, here, an optical recording medium having a single recording layer and an optical recording medium having two layers have been described as an example of an optical recording medium. However, an optical recording medium having three or more recording layers can also be used. is there.

It is a main block diagram which shows embodiment of this invention apparatus. It is a figure which shows the laser beam drive current Id for optimal reproduction | regeneration of a two-layer high-speed reproduction | regeneration optical recording medium. It is a figure which shows the laser beam drive electric current Id for optimal reproduction | regeneration of a single layer high speed reproduction or a two layer low speed reproduction optical recording medium. It is a figure which shows the laser beam drive electric current Id for optimal reproduction | regeneration of a single layer high speed reproduction or a two layer low speed reproduction optical recording medium. It is a figure which shows the laser beam drive electric current Id for optimal reproduction | regeneration of a single layer low-speed reproduction | regeneration optical recording medium. It is a figure for demonstrating the various optical recording media which can be optimally reproduced by this invention apparatus. It is a figure which shows the circuit example of a snubber circuit. It is a figure which shows the high frequency superimposed current amplitude characteristic of a laser drive circuit.

Explanation of symbols

2. Semiconductor laser element and snubber circuit (laser light emission circuit)
DESCRIPTION OF SYMBOLS 10 ... Objective lens 16 ... Main light detector 18 ... Sub-light detector 24 ... Drive control circuit (drive control signal output circuit)
26 ... Laser drive circuit 28 ... High frequency oscillator 30 ... Polarizing beam splitter 36 ... Signal reproduction system 38 ... Number of layers discriminating circuit 40 ... High frequency oscillator control unit (high frequency oscillator control circuit)
42 ... Optical system 50 ... Resistance means A for amplitude control ... Optical recording medium device Cs ... Capacitor D ... Optical recording medium Dr ... Recording layer Ib ... Basic current Id ... Driving current, laser driving current Irf ... High frequency current L ... Laser light LD ... Semiconductor laser element Ra1 ... First resistor Ra2 ... Second resistor Rf, Rs ... Resistor Sa ... Drive control signals Tr, Tr1, Tr2 ... Switching transistors (switching means)

Claims (3)

A laser drive current that suppresses ringing and overshoot using a snubber circuit is supplied to the semiconductor laser element, and laser light emitted from the semiconductor laser element is irradiated onto an optical recording medium having a single layer or a plurality of recording layers. An optical recording medium device having a configuration for reading out information,
A laser beam emitting circuit comprising the snubber circuit and the semiconductor laser element, and emitting a laser beam via an objective lens;
A main light detector that detects reflected light obtained by irradiating the optical recording medium with laser light emitted from the laser light emitting circuit and outputs a main detection signal according to a light reception level;
Based on a main detection signal output from the main light detector, a layer number discrimination circuit that outputs a discrimination signal that at least discriminates the number of recording layers of the optical recording medium;
A sub-light detector that detects a part of the laser light emitted from the laser light emitting circuit and outputs a sub-detection signal;
The laser light emission circuit so that the output power of the laser light emitted from the semiconductor laser element is constant based on the determination signal output from the layer number determination circuit and the sub detection signal output from the sub light detector. A drive control circuit for outputting a drive control signal to the input side of
A high-frequency oscillator is provided, and a basic current for driving the semiconductor laser element is formed based on a drive control signal output from the drive control circuit, and a high-frequency current output from the high-frequency oscillator is superimposed on the formed basic current A laser drive circuit for outputting the laser drive current obtained in this way to the laser beam emission circuit;
A high-frequency oscillator control circuit that outputs a control signal for changing the output current amplitude of the high-frequency oscillator to the high-frequency oscillator based on a determination signal output from the number-of-layers determination circuit;
The layer number discrimination circuit
When the optical recording medium is determined as a single-layer optical recording medium, a determination signal for operating the snubber circuit and reducing the output current of the high-frequency oscillator is controlled by the laser light emission circuit and the high-frequency oscillator control. Output to each circuit,
Further, when the optical recording medium is discriminated as a multi-layer and low-speed reproducing optical recording medium, a discrimination signal for deactivating the snubber circuit and reducing the output current of the high-frequency oscillator is emitted from the laser beam. Output to the circuit and the high-frequency oscillator control circuit,
Further, when the optical recording medium is determined to be an optical recording medium having a plurality of layers and reproducing at a higher speed than the low-speed reproducing, a determination signal for deactivating the snubber circuit and increasing the output current of the high-frequency oscillator Is output to the laser beam emitting circuit and the high frequency oscillator control circuit, respectively. The high frequency oscillator control circuit includes:
Switching means for turning on and off based on a discrimination signal output from the layer number discrimination circuit;
High-frequency current amplitude switching means for controlling the resistance value to be changed by turning on and off the switching means and controlling the amplitude of the high-frequency current output from the high-frequency oscillator to change according to the number of layers of the optical recording medium. The optical recording medium device according to claim 1. The laser beam emitting circuit is
A snubber circuit control unit for controlling the snubber circuit;
The snubber circuit control unit includes switching means for turning on / off based on a determination signal output from the layer number determination circuit;
By turning on and off the switching means, the snubber circuit composed of a resistor and a capacitor is connected in parallel with the semiconductor laser element, and the amplitude of the high-frequency current output from the high-frequency oscillator and flowing to the semiconductor laser element changes. 2. The optical recording medium device according to claim 1, further comprising a high-frequency current amplitude switching means for controlling the high-frequency current amplitude.

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